Bash/Sh incompatibilty

[Rainer Dorsch <rainer@rainer.informatik.uni-stuttgart.de>]

The question is somewhat off topic, but someone might know reference:

I set

export PS1='abc '

Then I start xterm and I get a bash with the same prompt.

When I do it via a script

 #!/bin/bash
 xterm

I get the standard prompt of bash (``\s-\v\$ '').

This behavior is incompatible with sh (on Solaris) and I do not understand, 
why bash behaves that way (Is there an application for this. I could always 
set PS1 in the script, if I explicitly want to do this, but the other way is 
more difficult).

Bash on Solaris show the same strange behavior.

Thank you.

--Rainer.